1. Field of the Invention
The present invention relates to a mobile communication system and relates in particular to a mobile communication system, gateway equipment, communication method and mobile terminal authentication method for mobile IP protocol.
2. Description of Related Art
Much intense study of IP (Internet Protocol) for mobile communication networks has been made in recent years.
The IETF (Internet Engineering Task Force) is working on standardized Mobile IPv6 specifications (for example, in non-patent document 1; Mobility Support in IVv6 draft-ieff-mobileip-ipv6-19.txt, Work in Progress).
The elements comprising the Mobile IPv6 network structure are a Mobile Node (MN), a home agent (HA), and a correspondent node (CN).
An IP address (home address serving as identification information for the mobile node) is assigned to the MN. This IP address does not change even when the MN moves. A link having the same prefix as the home address is called the home link. The HA manages MN location information (Binding Cache) located other than in the home link.
When the MN moves to a link (host link) other than the home link (foreign link), the MN acquires the IP address of that link. This address is called the Care of Address (CoA). The MN receives a router advertisement sent periodically by the router in the foreign link. The MN senses movement by detecting a prefix different from the home address.
When the MN detects movement, it registers the location in the HA. The MN contains a Home Agent Address Discovery function capable of dynamically searching for home agent IP addresses.
The MN creates a Mobile IPv6 Home-Agents Anycast Address from the prefix of the home link. The MN sends an ICMP Home Agent Address Discovery Request to that address. That ICMP Home Agent Address Discovery Request signal is sent to the HA in each of the home links. The HA that received the ICMP Home Agent Address Discovery Request sends an ICMP Home Agent Address Discovery Reply containing HA information to the MN. The MN acquires the address of the HA by extracting HA information from the ICMP Home Agent Address Discovery Reply signal. The MN makes a binding update (performs location registration) of the HA address it acquired.
When the HA receives the binding update, it retains the MN home address and the CoA binding information in the binding cache. The HA next acts as a proxy (on behalf of the MN, sending a Gratuitous Neighbor Advertisement to capture packets addressed to the home address of the MN.
The CN (correspondent node) is a peer node with which a MN is communicating.
The procedure used by the CN for sending a packet addressed to the MN is described next.
The CN sends a packet addressed to the MN home address. The HA that received the packet addressed to the MN home address, searches the binding cache, and acquires the CoA matching the MN home address. The HA attaches an IP header for the received packet and sends the encapsulated packet. The Destination Address of the external header is a CoA.
When the CoA addressed packet is received, the MN first removes (decapsulizes) the IP header that was attached and restores the original packet.
The home network might reattach a prefix. The Mobile IPv6 contains a function to notify the MN of the host network of prefix information for the home network. The HA checks the binding cache and notifies the MN in the binding update process with an MPA (Mobile Prefix Advertisement).
Technology for localized management of mobile communication based on Mobile IPv6 has been proposed (for example, in non-patent document 2; Hierarchical Mobile IPv6 mobility management (HMIPv6) draft-ieff-mobileip-hmipv6-07.txt Work in Progress).
The MPIPv6 contains a MAP (Mobile Anchor Point) between the HA and MN. The MAP provides that network with a local HA function. The MAP may also contain an AR (access router) under its control. The MN receives a router advertisement from the AR containing a MAP option, and acquires the IP address of the MAP. The MAP option contains the global address of the MAP, the MAP prefix, the MAP preference, and the number of hops to the MAP, etc. The MAP uses either of the following methods to notify the AR of MAP options.
(1) MAP distributes a router advertisement containing MAP options to the router (AR).
(2) MAP expands the router renumbering function for IPv6 and notifies the AR of the MAP options.
Instead of the MAP informing the AR of the MAP options, the network manager may set the MAP option information in the AR.
The information with the MAP options is stored when a MN compatible with HMIPv6 standards receives the router advertisement containing the MAP options. The MN (compatible with HMIPv6) generates a RCoA (Regional Core of Address) from the MAP prefix contained in the MAP option and the MN interface identifier. The MN also generates an LCoA (on-link CoA) utilizing prefix information contained in the router advertisement. The LCoA is equivalent to the CoA of the Mobile IPv6.
The (HMIPv6 compatible) MN first of all makes a binding update (location registration) on the MAP. The MAP manages the binding information along with the RCoA and LCoA of the MN. The binding update signal that the MN sends to the MAP contains bits showing the MAP binding update (registration information). The MN next performs the binding update in the HA. The HA manages the MN home address and the RCoA of the binding information. When the MN has moved within the MAP, the MN rewrites only the MAP location information.
The IPv6 address is specified in RFC2373. Three types of addresses; unicast, anycast and multicast are defined as IPv6 addresses. The unicast address contains three types (global address, site local address, and link local address) of addresses. The site local address can only be used within the site and is equivalent to an IPv4 private address (for example non-patent document 3).
The IPv6 Prefix Delegation Options for DHCPv6 (DHCP-PD) are also being evaluated. Here, DHCP-PD is a function that makes use of DHCP (Dynamic Host Configuration Protocol) to assign IPv6 prefix (group) to sites from the side handling address assignment. The delegating router and requesting router are the elements that make up the DHCP-PD. The requesting router makes a request to the delegating router to assign an IPv6 prefix (group). The delegating router selects an IPv6 prefix (group) and sends that prefix to the requesting router. This DHCP-PD is used for example by ISP (Internet Service Providers) when assigning a prefix to subscribers (as for example in non-patent document 4).
[Non-Patent Document 1]
D. Johnson and others, Mobility Support in IPv6, [online], Oct. 29, 2002, Internet address www.ieff.org/internet-drafts/draft-ieff-mobileip-ipv6-19.txt
[Non-Patent Document 2]
Claude Castelluccia and others, Hierarchical Mobile IPv6 mobility management (HMIPv6), [online], October 2002, Internet address www.ieff.org/internet-drafts/draft-ieff-mobileip-hmipv6-07.txt
[Non-Patent Document 3]
R. Hinden and others, IP Version 6 Addressing Architecture, [online], July 1988, Internet address www.ieff.org/rfc/rfc2373.txt
[Non-Patent Document 4]
O. Troan and others, IPv6 Prefix Options for DHCPv6, [online], Nov. 27, 2002, Internet address www.ietf.org/internet-drafts/draft-ieff-dhc-dhcpv6-opt-prefix-delegation-01.txt
The zone A and zone B are mutually connected and when a mobile node (MN) belonging to zone A has moved to zone B, the HA holding the location information (binding cache) for mobile nodes in zone A functions as a proxy for the MN.
The zone A and the zone B utilize site local addresses so a conflict might arise between the MN home address and the visited network address.
The Mobile IPv6 ensures the arrival of communications at the home address by supplying a permanent IP address (home address) to the MN that does not change even if the MN moves its location. The MN user can change the network settings containing the IP address if the MN is a personal computer, etc. However, when the home address of the MN is changed (rewritten), the problem arises that the arrival of communications at the MN cannot be guaranteed. Methods allowing the MN to acquire the home address have been considered in order to resolve this problem. However, Mobile IPv6 does not contain a function to dynamically assign home addresses to the MN.
The Mobile IPv6 prefix discovery function is provided to the MN registering the location information (binding update) in the HA. So prior to making the binding update (location registration), the MN cannot receive the signal (MPA) notifying it of home network prefix information.